Spongiform degeneration of neurons, which is the most characteristic and constant neurohistological lesion of prion diseases, consists of focal swelling of neuritic processes with loss of internal organelles. This suggests that the defects underlying spongiform degeneration and clinical signs in prion diseases involve altered ion channel function and triggering of calcium (Ca2+) activated degradative enzymes. In a preliminary study, we examined Ca2+ regulation in two cell lines chronically infected with scrapie prions using a laser-based image cytometer with Indo-1 fluorescence as an indicator of intracellular Ca2+ concentration [Ca2+]i. Specifically, control HaB cells had a broader spectrum of Ca@2+ regulatory mechanisms than control N2a cells. All of the Ca2+ regulatory mechanisms were severely depressed in both cell lines when infected with scrapie prions (ScHaB and ScN2a cells). ScHaB cells, but not ScN2a cells, developed cytopathology when exposed to high extracellular Ca2+. Here we propose experiments to verify the above findings; to test whether cellular degeneration on the one hand is due to prion infection related abnormalities in selective classes of Ca2+ regulation mechanisms; to test whether astrocyte proliferation, also characteristic of prion diseases, on the other hand is due to abnormalities in other classes of Ca2+ regulation mechanisms; and, whether cytopathology is due specifically to accumulation of PrPSc.